Hi Mary - very valuable comment! We have "experienced" the very situation
you detailed which is how we arrived at the gloves we use today. Always fun
to explain to a buyer that "all gloves are NOT alike!".
Dave
On Tue, Jan 14, 2020 at 2:17 PM Mary Davis <[log in to unmask]>
wrote:
> My experience indicates that nitrile gloves vary greatly from brand to
> brand, grade to grade, etc., and testing should be performed to qualify
> them prior to use. I wasn't dealing with silver corrosion - but instead
> with transfer of residue that caused de-wetting of urethane conformal
> coating and cure inhibition of silicones. I was told by a rep from the
> glove company that the residue transfer was the result of residual
> un-reacted nitrile. That seems to make sense as nitriles are listed as a
> source of silicone cure inhibition.
>
> Some nitrile gloves are washed as part of their manufacture. Some nitrile
> gloves are certified as containing low ionic extractable content. The
> washed and low ionic extractable gloves are relatively expensive but
> performed the best and prevented costly quality issues. And, once you get
> a nitrile glove product that is confirmed acceptable, you need to lock in
> your choice. Otherwise, time goes by and a buyer changes to a less
> expensive glove - and the quality problems return.
>
> Regards,
>
> Mary Davis
> Retired Materials and Process Engineer
>
> -----Original Message-----
> From: TechNet <[log in to unmask]> On Behalf Of Joe Russeau
> Sent: Tuesday, January 14, 2020 8:53 AM
> To: [log in to unmask]
> Subject: Re: [TN] [External] Re: [TN] Need advice : sulphur level on
> Gloves/ESD mat and reference standards
>
> I would add to this conversation by saying that we have tested power-free
> nitrile and powder-free vinyl gloves using ion chromatography for "ionic"
> contaminates. We analyze the lots of gloves we use to handle customer
> product to ascertain the types and amounts of ionics that we may be
> contributing to the test results. We have typically found that gloves of
> those types have very low levels of ionic contaminates (less than 1.5 ppm
> total for a pair of gloves anions and cations combined). Couple low ionic
> levels with proper handling techniques and you can minimize the chance for
> transference to a product.
>
> That all said, I can't speak to the relative amounts of contaminates
> coming from ESD mats. Until this past year, ESD mats haven't really been
> on anyone's radar for being a corrosion contributor. Now there seems to be
> a lot of questions being asked about the levels of contaminates coming from
> mats and do those contaminates lead to corrosion products. To date, I am
> not personally aware of any standard that defines what contaminate levels
> ought to be for mats. Perhaps some guidance is needed. My 2 cents would
> when in doubt have those materials
> tested, if for nothing else but peace of mind.
>
> Best Regards,
>
> Joe Russeau
>
> PAL, Inc.
>
> On 2020-01-14 10:55, David Hillman wrote:
>
> > Hi team - I'll just add a couple of comments to the conversation. The
> > tarnish typically found on immersion silver board finishes is the
> > result of boards being wet/damp from processing which leads to a
> > brown/black visual tarnish due to reactions with the air. The majority
> > of the time the tarnish is cosmetic and does not impact the
> > solderability of the board. If it is not cosmetic then you will find
> > the solderability is a problem pretty easily. The gloves we use are
> > not sulfur free - they are Micro Grip nitrile gloves from VWR
> > International (part number 40101-350) and we haven't seen an issue
> > with them causing tarnishing. Of course, everyone should be handling a
> > board by its edges as much as possible too. I would look at your board
> > storage and handling practices as possible root cause sources for the
> tarnishing. Good luck.
> >
> > Dave Hillman
> > Collins Aerospace
> >
> > On Tue, Jan 14, 2020 at 7:42 AM Douglas Pauls <
> > [log in to unmask]> wrote:
> >
> > "Last Century"? Thanks for turning me from old to ancient Bev.
> >
> > As Bev indicated, there are no standards in our industry for this kind
> > of thing. The recommended ionic levels from Foresite, PAL, or other
> > test labs are for circuit assemblies or bare circuit boards, not for
> > amounts in gloves. We use standard latex or nitrile gloves here and a
> > lot of what we use is immersion silver. We have not seen the need for
> special gloves.
> >
> > In terms of functional impact, if it is just tarnish, then there is no
> > functional impact. Silver oxide conducts as well as pure silver. All
> > you have is a cosmetic issue when people collectively lose their minds
> > looking at tarnished silver.
> >
> > I suspect what happened is somebody somewhere thought "sulfur is bad
> > for silver" (which it is), "so we need sulfur free gloves" (which you
> don't).
> >
> > *Douglas Pauls *| Principal Materials and Process Engr | Advanced
> > Operations Engineering
> >
> > *COLLINS AEROSPACE*
> >
> > 400 Collins Road NE, MS 108-101, Cedar Rapids, IA 52498 USA
> >
> > *Tel:* +1 319 295 2109 | *Mobile: *+1 319 431 3773
> >
> > [log in to unmask]
> >
> > [log in to unmask] for all Export Compliant Items
> >
> > On Tue, Jan 14, 2020 at 7:31 AM Bev Christian
> <[log in to unmask]:
> >
> > First, do you like to be call GA or Tan?
> > a) & b) There are no standards. Shoot, we don't have any "official"
> > standards for sodium, potassium, fluoride, chloride, bromide, nitrate,
> > nitrate, phosphate or sulfate; unless they are in IEC standards that I
> > don't know about. We have the suggestions of Doug and Terry from the
> > last century and those from Delco and a couple of other sets.
> > Certainly the measurement of Doug Pauls, etc. are professionally
> > carried out.
> > c) Only cosmetic
> >
> > I have never heard anyone ask for sulfur free gloves. I am not aware
> > of what is available. I would start with asking a VWR or Fisher rep
> > (large chemical suppliers with extensive catalogues) .
> >
> > Regards,
> > Bev
> >
> > -----Original Message-----
> > From: TechNet <[log in to unmask]> On Behalf Of Tan Geok Ang
> > Sent: January 14, 2020 6:34 AM
> > To: [log in to unmask]
> > Subject: [TN] Need advice : sulphur level on Gloves/ESD mat and
> > reference standards
> >
> > Will really appreciate advice on the following;
> >
> > a) how much of sulphur/calcium, etc. on gloves/ESD Mat is acceptable
> > and what level is considered harmful in handling of PCBA/module with
> > sliver plated surface
> >
> > b) whether there are any "standards" or references for "compliance"
> > check for sulphur, and is there such measurements professionally
> > carried out
> >
> > c) What will be the impacts on the PCBA when silver plating become
> tarnish?
> >
> > There are sulphur free gloves but it is not easily accessible/available
> in Singapore and it is expensive.
> >
> > Thanks.
> >
> > GA Tan
>
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